In many wireless communication systems, a frame structure is used for data transmission between wireless stations such as a transmitter and a receiver. For example, the IEEE 802.11 standard uses a frame structure in a Media Access Control (MAC) layer and a physical (PHY) layer. In a typical transmitter, a MAC layer receives a MAC Service Data Unit (MSDU) and attaches a MAC header thereto, in order to construct a MAC Protocol Data Unit (MPDU). The MAC header includes information such as a source address (SA) and a destination address (DA). The MPDU is a part of a PHY Service Data Unit (PSDU) and is transferred to a PHY layer in the transmitter to attach a PHY header thereto to construct a PHY Protocol Data Unit (PPDU). The PHY header includes parameters for determining a transmission scheme including a coding/modulation scheme. Before transmission as a packet from a transmitter to a receiver, a preamble is attached to the PPDU, wherein the preamble can include channel estimation and synchronization information.
Data applications such as Internet web surfing and e-mail exchange usually require random wireless channel access with bursty traffic characteristics. Reserving a channel time allocation (CTA) in advance for these types of data applications may lead to low MAC layer efficiency. Conventional channel access methods such as carrier sensing multiple access/collision avoidance (CSMA/CA) and an optional mechanism of Request To Send/Clear To Send (RTS/CTS) at a Contention Access Period (CAP), are impractical due to the high interference and collision probability caused by asymmetric antenna system (AAS) and directional transmissions.